1. Technical Field
The present disclosure relates to a surface roughening apparatus for a metal stock and a surface roughening method for a metal stock, and more particularly, to a surface roughening apparatus and a surface roughening method for roughening a surface of a metal stock.
2. Description of Related Art
It is known that in the case of bonding a metallic material and a resin to each other, the surface of the metallic material is roughened to increase the surface area, which leads to an improvement in bonding strength. Examples of the roughening method include methods using a laser, etching, and shot blasting. However, in the method using a laser, an increase in processing time and an increase in equipment cost cause an increase in manufacturing cost. In the method using etching and the method using shot blasting, convex and concave portions formed on the surface of the metallic material have a small depth, which may make it difficult to obtain a sufficient bonding strength.
It is also known that in the case of roughening a surface of a metallic material, a recess (concave portion) formed on the surface of the metallic material is formed in an “undercut shape”, which leads to a further improvement in the bonding strength. The “undercut shape” refers to a shape in which a middle part of a wall surface forming a recess projects (outstands) inwardly (toward the hole of the recess, i.e., toward the center of the recess). In the case of bonding the metallic material and a resin to each other, the resin is made to flow into the recess. Thus, even if a force acts in a direction in which the resin is separated from the metallic material, the resin hooks at the undercut shape, which prevents the resin from being separated from the metallic material. This leads to a further improvement in the bonding strength.
In connection with the technique described above, Japanese Unexamined Patent Application Publication No. 2011-005549 discloses a method of roughening metal surfaces to improve the adhesion of layers thermally sprayed thereon. In the method disclosed in Japanese Unexamined Patent Application Publication No. 2011-005549, ridges which are formed between grooves formed in the metal surface are plastically deformed to form undercuts in the grooves.